1. Field of the Invention
The present invention relates to a method and a system for detecting a crank angle of an engine. More particularly, the present invention relates to a method and a system for detecting a crank angle of an engine, which are capable of avoiding false detection of a non-tooth position of a crank pulse rotor.
2. Description of the Background Art
There is a known method of detecting a crank angle through an output signal from a crank angle sensor arranged at a position facing a crank pulse rotor attached to a crankshaft of an engine. The crank pulse rotor includes a plurality of teeth, or protrusions, formed at predetermined crank angle intervals (for example, 30 degrees) on an outer circumference thereof. The crank pulse rotor also includes a non-toothed portion formed on a portion of the outer circumference thereof.
The crank angle sensor outputs a crank pulse when the crank angle sensor detects presence of each tooth. A crank pulse interval in the non-toothed portion is longer than a crank pulse interval in the toothed portion of the crank pulse rotor. Accordingly, each crank pulse is assigned to a stage number based on the non-toothed portion to determine crankshaft angle, and to perform fuel injection control and ignition timing control of the engine.
There are a number of ways of determining a timing, at which a position of the non-toothed portion of the crank pulse rotor can be set in a cycle of the engine, among various timings in a cycle of the engine. The layout of the non-toothed portion can be determined, for example, by mainly aiming at accurate detection of ignition timing. In this case, the non-toothed portion can be set to correspond to the valve opening start timing of an inlet valve.
In other words, for the purpose of reducing an error at starting energization, the non-toothed portion can be set not to correspond to the energization start timing of a spark plug. However, if the non-toothed portion is set not to correspond to the energization start timing, then the non-toothed portion corresponds on a valve open period of the inlet valve. Accordingly, even if the throttle opening drastically increases during the open period of the inlet valve, such a change cannot be detected, thus causing lean combustion in some cases.
It is desirable to prevent lean combustion at a time of rapid acceleration, and to enhance the drivability of the vehicle by modifying the position of the non-toothed portion in consideration of fuel injection. Specifically, when the non-toothed portion is arranged to correspond to the valve opening start timing of the inlet valve, calculation of additional fuel injection and injection based on the calculation can be performed in response to a change in throttle opening even after starting opening state of the inlet valve, thereby preventing lean combustion.
A controller of a single-cylinder 4-cycle engine is disclosed in Japanese Patent Laid-open Publication No. 2007-182797. The controller includes an apparatus for determining strokes based on the crank pulse intervals in relation to the difference in crank pulse interval throughout the individual strokes of the engine. In the apparatus of Japanese Patent Laid-open Publication No. 2007-182797, the non-toothed portion is set not to correspond to the ignition timing.
However, when the non-toothed portion is laid out so as to come in front of the crank angle sensor at a time of opening the inlet valve, the non-toothed portion does not correspond to a time just after a top dead center (TDC) position.
Accordingly, especially in case of a single-cylinder 4-cycle engine, the crank pulse intervals largely differ between just before and just after the TDC position. This causes disadvantages in detecting the non-toothed portion based on the degree of change in pulse interval before and after the non-toothed portion. Specifically, the position at the TDC could be falsely detected as the non-toothed portion.
The present invention has been made to overcome such drawbacks of the method of detecting a crank angle of an engine. Accordingly, it is one of the objects of the present invention to provide a method and a system for detecting a crank angle of an engine, which are capable of accurately distinguishing a non-toothed portion of a crank pulse rotor, and the TDC position thereof even with a layout in which the non-toothed portion corresponds to a valve open period of an inlet valve of an engine.